1. Field of the Invention
The invention relates to the usage of the vertical blanking period of a video signal. More specifically, the invention relates to the use of the vertical blanking period of a video signal when transmitted over a wireless channel.
2. Discussion of the Prior Art
In many homes, television and/or video signals are received through cable or satellite links at a set-top box which is located at a fixed point in the house. In many cases, it is desired to place a screen at a point that is a distance from the set-top box by a few meters. This trend is becoming more common as flat-screen televisions having a plasma or liquid crystal display (LCD) are hung on a wall. Connection of the screen to the set-top box through cables is generally undesired for aesthetic reasons and/or installation convenience. Thus, wireless transmission of the video signals from the set-top box to the screen is preferred. Similarly, it may be desired to place a computer, game controller, VCR, DVD, or other video source that generates images to be displayed on a screen a distance from the screen.
Wireless short range transmission in the home is possible over the unlicensed bands around 2.4 GHz or around 5 GHz e.g. in the U.S 5.15-5.85 GHz band. These bands are currently used by wireless local area networks (WLAN), where the 802.11 WiFi standard allows maximal data rates of 11 Mbps (802.11b) or 54 Mbps (for 20 MHz bandwidth using the 802.11g/802.11a standards). Using the emerging Multi-Input Multi-Output technology, the data rate of the emerging 802.11n standard is increased to around 200 Mbps. Another alternative is to use Ultra Wide Band (UWB), which claims to provide a data rate of 100-400 Mbps.
Techniques for transmitting an essentially uncompressed video signal are disclosed in a PCT patent application IL/2004/000779 entitled Wireless Transmission of High Quality Video (hereinafter the ‘779 application’) and in U.S. patent application Ser. No. 11/551,641 entitled Apparatus and Method for Uncompressed, Wireless Transmission of Video (hereinafter the ‘641 application’), both assigned to common assignee and both of which are incorporated here in by this reference thereto.
In a video signal there are well known time periods referred as the vertical and horizontal blanking periods. These blanking periods were originally designed for that period in time during which an electron beam of a cathode ray tube (CRT) was allowed to move back to an initial position and restart its tracing across the screen. The duration of the horizontal blanking period is shorter than the vertical blanking period. As determined by all video transmission standards, during these periods no video data is transmitted and therefore no use is made of the wireless channel. This also applies to digital video format standards, such as HDMI, DVI, SMPTE 274M, SMPTE 296M, and the like.
Specifically, a typical video sequence is fragmented to video frames, as shown in FIG. 1. Each video frame, for example video frame 110, that normally lasts 16.6 milliseconds, is divided into a video data period, for example period 112, of approximately 96% of the entire time period, and vertical blanking period, for example period 114, of approximately 4% of the entire time period. As previously noted, this period was originally conceived for the mechanical movement of the beam in a CRT from the end of the video portion of the frame, for example frame 110, back to the beginning of the immediately subsequent frame, for example video frame 120.
In order to utilize the transmitting bandwidth, solutions suggest the use of the vertical blanking period for a plurality of purposes. For example, this period may be used for the purposes of video transmission. This use, however, requires large buffering for the purpose of spreading the transmission over 100% of the frame time. The buffering is required at both the transmitter and receiver further increasing the expense in providing such solution.
It would be advantageous for wireless video systems, for example those disclosed in the '779 application and the '641 application, to make use of the period where no video data is to be transmitted, for purposes unique to issues related with such wireless transmission. For example, the invention has recognized that it is possible to overcome prior art limitations when handling wireless modems during the transmission of valid data to reduce the effective channel bandwidth.